1. Field of the Invention
The present invention generally relates to coin detecting, discriminating and testing devices, and is more particularly directed to apparatus for testing a coin for the purpose of accepting or rejecting the same in a coinoperated vending machine, game, telephone or the like.
2. State of the Prior Art
Coin-operated equipment or machines are usually equipped with a device which tests any coin inserted therein. Various devices have been used in the past which embody some type of mechanical or electronic testing apparatus for discriminating against foreign coins or slugs.
Numerous types of devices are known and have been used in the past for such purposes. Exemplary of the state of the art is applicant's U.S. Pat. No. 3,901,368, the patents referred to therein and a number of subsequent patents. U.S. Pat. No. 4,234,071 issued to Le-Hong also discloses a device for checking metal pieces and particularly coins. It uses the technique of U.S. Pat. No. 3,901,368 with additional means for testing a coin in predetermined position as the coin passes.
Applicant's prior patent discloses a coin acceptor/rejector comprising a reference oscillator tuned to a fixed predetermined frequency and a current output stage driven by the reference oscillator and having a sensing tank circuit head adapted to resonate at or near the oscillator frequency when the desired coin is inserted in the vicinity of the inductor of the sensing tank, the latter inductor being mounted in the path of the coin within the coin operated device. The voltage developed across the tank circuit is measured and compared to a reference voltage derived from the common voltage supply to obtain a narrow amplitude detection band within which the tested coin is accepted. If the amplitude of the oscillations in the sensing tank circuit either exceeds or falls short of the detection band limits, the coin is rejected.
For optimal performance of the circuit it is critical to maintain the width of this amplitude detection band as narrow as possible in order to positively discriminate against coins or slugs approximating the characteristics of the desired coins. This requirement in turn creates high stability requirements and the circuit must be made as nearly insensitive to parameter changes as is possible to avoid drift of the very narrowly defined voltage levels at which the coin will be accepted. This is accomplished both through symmetrical and balanced design of the circuit with low drift components as well as through careful construction and positioning of the oscillator coil and sensing coil of the amplifier tank circuit.
The technique disclosed in applicant's prior patent benefits from working across the resonance characteristic of the sensing tank circuit to increase selectivity and to yield large signal levels able to be directly discriminated with minimum components. The coin diameter, thickness, and permeability yield an effective sensing coil inductance, and the coin's resistivity contributes to the effective sensing tank circuit lossiness (or Q).
The combination of effective inductance and lossiness of the sensing tank circuit yields the signal amplitude to be tested. Since a single amplitude test is performed to accept the coin, a slug made of a different metal, having a different effective inductance and lossiness, could be tailored to result in the acceptable signal level. The following invention does not have this limitation.